For all you folks out there that have fabricated your own extractors, what size primaries have you used? different engines and size (bore,exhaust and inlet ports and valves etc) will definatley all matter in the different size but how big were/was they?

I'm gona make my own as the cars off the road for another 3 months so got some time to kill and i am using a 1 3/4" sports exhaust and have had some extra swirl on the head but valves are the same...I was thinking primarys about 35 - 40 mm? And what length were the pipes going to the collector for 4 - 1 and 4 - 2 - 1 as i havent decided yet what to do..
My metal work teacher says do 4-2-1 as there better for street and below 6000rpm application as 4-1 are more for above this yes? I really need to know the length of the headerss as all pipes have to be practically exact same length for the 'scavenging' affect and no back pressure to work........

Cheers
Dave

firstly, whay are you doing this? to save money?

I think you'd be better off scrounging up a secondhand set. If the bottom is a bit rusty around the collector you can always just remanufacture that part.

You'll end up with a better result both for aesthetics and performance. Manufacturers will have put far more thought into their designs than you can possibly learn about here.

for one: to save money & two: the others i have dont fit (they hit the intake manifold, bout 2cm gap between that and the head) and plus their pretty dodgy quality with rust in the critical areas and the collector is about to fall off.......not too flash hot!

I have good advice as the guy who is helping me at school is a fitter & machinist by trade who has 25yrs+ with performance and stock 4 cylinder cars who has owned a P510 (L18 tho...)
He said that i only need to know the length of what pipes people have used, how much clearance (strut tower, mounts, firewall, g/b) and what size primaries but 35ish sounds good as my valves are stock
I dont wana get ripped off again really and dont have 250+ dollars to fork out for another set (even the others were only 50 bux!)......

Cheers
Dave

why can't you copy the lengths of the set you already have? As I said before, the exhaust manufacturers will have put more thought into the design of those pipes than you can learn here - header design is quite involved.

I encourage you to build your own headers, you'll learn alot about welding and construction and that is never a waste. You'll also have something unique. That said, production headers are a compromise. Theory touts equal length primaries, but seldom does a set of headers costing less than $500 have equal primaries. Does it really matter? No, not really unless you're chasing all the miniscule horsepower you can. By constructing your own though, you can pay attention to alot more detail than a sweatshop header manufacturer will. In addition, you can tune to an operating range that may not be available off the shelf. Ever see a set of headers for an A series made of stainless or inconel? I would suppose they are quite rare. By building your own, you can choose your material. I say go ahead and build you own. Look for some books online with header formulas and construction techniques. Draw up your primary mounting flange in cad and get it milled, laser cut or water jetted. A 4-2-1 header would do well on an A series. Spend your extra money getting them ceramic coated and they will last you a lifetime, or darn near. By all mean, have fun and learn alot.

Yeah im going to tackle it full on and hoping that the end result will be more than satisfying!!!
The choice of materials the usual steel i reckon but i will jet hot coat it when done for better heat retaningidge. I reckon i will go for the 4-2-1 exercise and the bends will be the worst as we have no tube bender so will opt for the old sand in the tube and oxy effect they used to do for extractors....
Any other snags i should be looking out for? I reckon i'l guide the 2 headers into a bigger pipe instead of using a flange for both collectors then run one big one to the exhaust system, this sound gewd? Like the legendary errol has done here...
http://www.datrats.com.au/FIA-EXTRCTR-2.JPG
Not datsun xtractors i know but same idea...

Cheers
Dave

Quote:

how does this work then?
I've never tried to make a set of headers, I'm with L18 B110 in that I think it is better to just buy a set, they are only about half the price you said, but, I definitely don't want to put you off the idea, and best of luck and let us know how you get on (with pics!), but I think bending exhaust tube without a proper bender without crushing the tube would be tricky...

Instead of bending your headers, I would suggest buying the bends. Get some 45's and 90's and cut off what you don't need. Too bad your not in the States, Stahl has a box of misbent tubing and you could probably do several headers.

http://www.stahlheaders.com/Frame%20Tubing.htm

You can also buy the merged portions too, but by using steel you could also make your own fairly easy. In this pic, you can see that they used small straight and curved sections to make the header. It'd be alot easier than trying to bend each pipe kink-free in one piece.

http://www.magnumforceracing.com/services/headers_FALCON.htm

This is the easy way as you can make the flange and tack a piece at a time on while checking for fit. If you get into a bind, you can always backtrack a section or two. You'll refine your tig experience undoubtedly. Pay attention to how you are going to weld each joint. Make a couple of test pieces so you can check the inside of the tube, you want a smooth transition. The curves will need a little persuasion where they meet the straights as the cross section of the curve isn't exactly round. Patience and fit are the keys.